In a thermocouple, a voltage is generated by providing a difference in temperature between the opposite ends thereof. This is due to the Seebeck effect, and can be utilized for a device designed to extract the voltage as electric energy. The thermoelectric power generator wherein heat energy can be converted directly into electric energy has attracted much attention as effective means of utilizing heat energy, as represented by the case of waste heat utilization.
Meanwhile, the flow of a current caused to occur through a thermocouples results in generation of heat at one end thereof, and absorption of heat at the other end thereof. This is due to the Peltier effect, and a cooler can be manufactured by utilizing such phenomenon of heat absorption. This type of cooler which does not comprise mechanical components and can be reduced in size has an application as a portable refrigerator, or a localized cooler for lasers, integrated circuits, and the like.
Thus, a power generator or a cooler (thermoelectric device) made up of a thermoelectric element such as thermocouples is simple in its construction, and is in a more favorable condition for miniaturization as compared with other types of power generators or coolers, offering high usefulness. For example, with the thermoelectric device for use in the thermoelectric power generator, there will not arise a problem of leakage of electrolyte or depletion of power as with the case of a redox cell, and the thermoelectric device has therefore promising prospects for application to portable electronic apparatuses such as an electronic wrist watch.
The general construction of a conventional thermoelectric device has been disclosed in, for example, Japanese Patent Laid-open No. 58-64075 , in which thermoelectric semiconductors of two dissimilar conductivity-type, p-type and n-type, are alternately and regularly arranged so that a multitude of thermocouples are formed in a two dimensional arrangement, and each thermocouple is electrically connected to the other in series through electrode plates.
In this construction, the thermoelectric device is formed in a board-like shape by the thermocouples in a two-dimensional arrangement. The upper surface and the under surface of the thermoelectric device becomes faces on which hot junctions and cold junctions of the thermocouples are located, respectively. In a case of a thermoelectric generation device, the thermoelectric generation is caused to occur by a difference in temperature between the upper surface and the under surface of the device.
Since portable electric apparatuses, having an expectation that such thermoelectric devices will be applied thereto, are usually used at around room temperature, it is not expected to obtain a sufficient degree of temperature difference inside of the portable electric apparatus. For example, in the case of a wrist watch, the temperature difference obtained in the watch through a body temperature and the ambient temperature will be 2.degree. C.
However, an output voltage of a thermocouple, even using a BiTe-based material which is said to have the highest figure of merit at around room temperature, is about 400 .mu.V/.degree. C. per couple, so that when the thermocouples using the BiTe-based material are incorporated into a wrist watch, an output voltage obtained is only 800 .mu.V per couple. Therefore, in order to obtain voltage over 1.5 V, which is necessary for driving the wrist watch, not less than about 2,000 couples of thermocouples are required to be incorporated.
Furthermore, in the case of an electronic wrist watch, wherein mechanical components and electric circuit components as well as the thermocouples need to be encased therein in spite of a small and limited internal volume thereof. Accordingly, an essential condition is that the design of a thermoelectric device itself be as small in size as possible.
Meanwhile, wiring is required for an electrical connection between the thermoelectric device and external circuits, and thus, as disclosed in aforementioned Japanese Patent Laid-open No. 58-64075, the connection is performed by respectively connecting lead wires to electrode plates located at both ends of a set of thermocouples connected in series.
As described hereinbefore, when a thermoelectric device is incorporated into a wrist watch, it is required that the thermoelectric device is designed to be as very small in size as possible, and additionally, a desired voltage can be obtained. However, as the thermoelectric device is decreased in size, the electrode plates for outputting voltage is reluctantly required to decrease in size.
In consequence, it would be extremely difficult to connect a lead wire onto the electrode plate so as to establish connection with the external circuit. In other words, it would be difficult to execute electrical connection between the thermoelectric device and the external circuits, which is necessary to practical use, resulting in difficulties of incorporation of the thermoelectric devices into portable electric apparatuses expecting of application.